13 



large number of berries affected with Stilbella examined no others with 

 Sphaerostilbe were found, so that even if it were a stage of Stilbella 

 it could play a very small role in the distribution of the disease in 

 this island. If the fungus is a Basidiomycete, as assumed with some 

 reason by Spegazzini/ it was not found to possess such a stage. 



It is of interest to note that, although the coffee plant is the princi- 

 pal host of this fungus, numerous other plants are also affected to 

 some extent. The writer has found it on such unrelated host plants 

 as the orange, mango, Begonia, various ferns, several of the coitres 

 {Commelina spp.), and guava {Inga vera), and bejuco de carro 

 {Velia sicyoides), and have noticed the spots, but not fruits, on the 

 yautia, banana, and also on several wild plants. The coitres, which 

 are perhaps most affected, and the ferns and other plants of low habit 

 of growth form in many places a continuous ground covering and 

 catch the greater part of the falling propagative bodies which escape 

 the coffee leaves, and are hence peculiarly subject to the disease. 

 They are apparently able to communicate it to unaffected plants of 

 the same kind and doubtless also to healthy coffee plants. There were 

 noticed places where the coffee was not attacked until several weeks 

 after the ground plants had become infected. 



When first taking up the study of coffee diseases in Porto Rico 

 the " mancha de hierro " appeared of small importance, for the reason 

 that the area affected is so restricted by climatic conditions. But the 

 regions of the island most affected produce the best coffee, and if it 

 were not for this disease they would give larger yields. The injury 

 to the trees is not so much in the actual amount of the leaf tissue 

 destroyed, although this may amount to one-fifth or even more of the 

 entire amount^in the worst cases, but in the defoliations which take 

 place after a time. The diseased leaves drop sooner than those not 

 affected, and owing to the weakened condition of the tree are not soon 

 replaced. After the first severe attack the base of each tree may be 

 seen to be surrounded by a pile of green leaves several inches deep. 

 The disease never kills the trees. They live on with scanty foliage 

 and are able to put forth some new growth and bear a small amount 

 of berries each year. 



The decrease in yield following an attack of the leaf spot is marked. 

 In one experimental plat, where a record of the yield had been kept 

 for some years, it was found to be 75 per cent. In this case the dif- 

 ference between the trees before and after the attack was such as 

 accompanies the loss of the greater part of the foliage. 



The fungus, Stilbella, also attacks the berries. As mentioned 

 above, however, it does not do very much harm to the fruit — much 

 less, in fact than that caused by the Cercospora fruit spot — for it 



iRev. Facult. Agron. y Vet, La Plata, 2 (1896), No. 22, p. 339. 



